Nondefoliating Pathotypes of <i>Verticillium dahliae</i> Races 1 and 2 Causing Verticillium wilt and Mortality of <i>Ailanthus altissima</i> in Northeastern Spain

Verticillium wilt on the invasive plant species, <i>Ailanthus altissima</i>, has been reported in Europe and USA. Symptoms of the disease in northeastern Spain were first observed in 2007, and it has progressively expanded within this region thereafter. In this work, ninety-two <i>Verticillium</i> isolates were recovered from diseased <i>Ailanthus</i> trees in four riparian-forested sites in the Girona Province of northeastern Spain. Identification of <i>Verticillium</i> field isolates to species was based on morphological traits and species-specific PCR assays. All isolates were identified as <i>V. dahliae</i>, which was consistently recovered from all surveyed diseased <i>Ailanthus</i> stands, supporting its strong association with <i>Ailanthus</i> decline in the region. The use of race-specific molecular markers revealed the presence of races 1 and 2 in <i>V. dahliae</i> populations from <i>Ailanthus</i> in Spain; however, only a single race was present at each of the sampled locations. Furthermore, PCR-based assays designed to differentiate defoliating and nondefoliating <i>V. dahliae</i> pathotypes indicated the exclusive presence of the nondefoliating pathotype in <i>V. dahliae</i> populations from <i>Ailanthus</i> in the region. All isolates were pathogenic and virulent on <i>Ailanthus</i> seedlings, severe wilting, defoliation and occasional plant death were observed 90 days after inoculation regardless of the race. The race and pathotype structure of the <i>V. dahliae</i> population from <i>Ailanthus</i> had not been investigated previously. These findings confirm the widespread occurrence of Verticillium wilt caused by <i>V. dahliae</i> in <i>Ailanthus</i> in Europe and provide new insights into the population structure of this pathogen on natural stands of this invasive plant species.